1. Field of the Invention
The present invention relates generally to the field of radar cross-section/radar signature measurements and, in particular, to an improved radar signature evaluation apparatus for measuring and evaluating the radar signature of an aircraft, missile, and the like.
2. Description of the Prior Art
The role of radar to perform all-weather surveillance, detection and tracking of potentially hostile aircraft, missiles or other airborne vehicle was established during the second World War. In response to the availability of highly sophisticated radar systems to hostile forces over the past two decades, survivability has become a critical aspect of all military vehicles. For example, stealth or low radar observable aircraft, such as the B-2 bomber and the F-117 fighter aircraft, were developed to evade the radar of forces hostile to the U.S. military.
Because the principal component of survivability is low radar-observability (L.O.), state of the art military systems involve complex designs, such as the delta shaped designs of the B-2 and F-117 aircraft, to provide for low radar signature. The development of low radar-observability aircraft and other vehicles requires efficient methods for testing, analyzing, interpreting and diagnosing the radar signature performance of these aircraft and other vehicles.
Radar signature, or radar reflectivity, of an aircraft or other vehicle describes how it will appear to an observing radar and thus, determines its detectability. Due to the coherent nature of radar signals, a radar signature is a complex quantity, highly dependent on the viewing aspect, radar frequency and polarization of an aircraft or other vehicle. For example, the characterization of a typical aircraft viewed over all aspect angles and all frequencies over conventional frequency bands would require in excess of 10 million independent data samples. The vast amount of information required to completely characterize the radar signature of a complex aircraft or other vehicle taxes both computational and experimental means of obtaining the required data. Although computational methods are convenient, the bulk of radar signature information is obtained by experimental methods on specialized RCS (radar cross section) measurement ranges. The need to collect the vast amount of required data experimentally has been the driving factor for the development of specialized, high-speed instrumentation systems for the collection. These systems provide the raw data that is subsequently processed, analyzed, and interpreted to define the radar signature of the aircraft or other vehicle.
Radar signature information collected in the past was typically presented by line plots showing the magnitude of the radar return as a function of viewing angle of the aircraft or other vehicle. These plots, known as RCS patterns, were easily interpreted by individuals familiar with their significance. The need for and availability of the vast data volumes necessary for the evaluation of the modern systems require that the information be presented by vastly more effective means. In order to analyze, interpret and diagnose potential problems in radar signatures, the individuals, such as the scientist and engineers, who analyze radar signatures need display methods or techniques for conveying the maximum amount of information in a very concise and clear format to avoid being overwhelmed by the information.
The present invention overcomes some of the difficulties of the past, including those mentioned above in that it comprises a highly effective radar signature evaluation apparatus for measuring and evaluating the radar signature of an aircraft, missile, and the like. An instrumentation system, which includes transmitting and receiving antennas as well as a frequency translator and an I/Q demodulator, provides the means for generating the radar cross section data to be processed by a central processing unit/digital computer.
The transmitting antenna transmits a pulse of RF (radio frequency) energy in the direction of the test vehicle. The receiving antenna receives the reflection of the pulse from the test vehicle and provides it to the frequency translator. The frequency translator compares the transmitted and received RF signals and provides an IF signal which represents the phase and the amplitude difference between the transmitted signal and the received signal. The I/Q demodulator extracts the I and Q components from the I/F signal, the I and Q components are converted to a digital format and then supplied to a sample and store circuit. The sample and store circuit samples the digitized I and Q components and then stores the digitized I and Q components for each sample of radar signature data. The digital samples of radar signature data are then provided to a central processing unit which processes the radar signature data.
The processed radar signature data which includes frequency and angular data is displayed by a variety of plots by a printer or a display connected to the central processing unit. The plots provide both spectral and spatial representations of the radar signature, the spectral representations relating to frequency dependence of a scattered radar signal and spatial representations relating to a spatial distribution of scattering features of the airborne or other type of vehicle under evaluation.